Since my seller told me, that that original Twizy cargo bag is dicountinued,
I have menaged to found another backpack to fit in.
Now I know, it's NIKE elite max backpack and found realy nice and cheap copy option. When I made purchase I realy didn't know that's a Nike copy. There was no NIKE sign in the listing pics
This is how I secured it with locked rear seat backrest
Extra secured with two carabins
And how it looks in general
Like the original one that's not realy theft-proof, but where I live, it realy don't need to be.